Monday, March 17, 2008

Advice to the New Thorium Industry

Blogging can be an adventure. A week and a half ago, I wrote about the abundance of uranium and thorium. The evidence pointed to uranium being so abundant as to be all practical purposes, a renewable resource. In contrast the USGS reported thorium reserves seemed rare. Yet it was universally acknowledged that thorium was at least three times as plentiful as uranium. This made no sense. Then I found a report by Conrad Windham on thorium resources. Conrad Windham is a speculator, not a geologist, but Windham reported a tremendous geological find at Lemhi Pass in Idaho. According to Windham, there was enough thorium in the ground there to power the United States for several centuries, and quite possibly enough to power the United States for over 2000 years. Subsequently I found similar statements from Jack Loften. Loften had attended a meeting of geologists at which a paper on the Lemhi Pass find was read and discussed. Finally I located a confirmation of the Lemhi Pass find on the the Web pages of Thorium Energy, the owner of the Lemhi Pass stake. So It is beyond reasonable doubt Thorium Energy is the owner of a very large thorium find.

The implication of the Lemhi Pass are staggering. There are many advantages to the use of thorium rather than uranium in the nuclear fuel cycle. The thorium fuel cycle largely solves the problem of nuclear waste, it is proliferation resistant, and inherently safe thorium fueled reactors have been designed and tested.

The problem for Thorium Energy is not going to be getting the thorium out of the ground, indeed they are claiming a potential of "25 to 63 percent thorium oxide (ThO 2) per ton of raw ore. Thus one ton of thorium ore could potentially yield as much as 500-1,200 lbs. of high grade thorium oxide (ThO2)." The problem then will be finding the reactors into which the thorium will go.

There are several obstacles to the massive potential sale of thorium that are possible given the extent of the Lemhi Pass resources. The Light Water Reactor (LWR), the type of reactor used by the nuclear industry is extremely expensive. There are are numerous inefficiencies associated with the LWR concept. The LWR uses its fuel very inefficiently, and indeed most of the potential energy in its fuel is not extracted by the LWR. The inefficiency of the LWR fuel cycle in turn creates the problem of nuclear waste.

A second inefficiency has to do with reprocessing nuclear fuel. The solid reactor fuel in light water reactors must be broken down into a liquid soluble form, and chemically processed. This chemical processing of highly radioactive fuels is highly expensive. A more efficient reactor design would use fuel in a form that would me more easily to process chemically.

Finally, the LWR is inefficient in its use of the heat it produces. The LWR is limited by the use of water as a heat transfer medium. Water is not a very efficient means of transferring the heat nuclear fuel is capable of producing. Yet the higher output heat leads to greater the output heat from a reactor, the greater its thermal efficiency. Thus a more efficient reactor would use a heat transport fluid that is more efficient than water.

Paradoxically the inefficiencies of LWR contribute to the expense of building them, and create many of their problems. The inefficiencies of the light water reactor are the greatest obstacle to the the sale of thorium.

Jevons added: "It needs but little reflection to see that the whole of our present vast industrial system, and its consequent consumption of coal, has chiefly arisen from successive measures of economy."

"Civilization, says Baron Liebig, is the economy of power, and our power is coal. It is the very economy of the use of coal that makes our industry what it is; and the more we render it efficient and economical, the more will our industry thrive, and our works of civilization grow."

The lesson to the thorium produces is clear, if you want to sell more thorium, greater reactor economies are required. Those efficiencies are to be found in the management of heat, and in the processing of fuel, as well as in other aspects of reactor design that can lower reactor cost.
Reactor scientist at Oak Ridge National Laboratory, during the 1950's, looked at the problem of reactor design. They had invented the light water reactor, but were acutely aware of its limitations. They believed that reactors could be more efficient if the nuclear fuel were suspended in a fluid, rather than inserted into the reactor in a solid form. By suspending the fuel in a fluid, it became more easily accessible for chemical processing. After some research, they determined that the best fluid for this purpose was hot liquid fluoride salts. A test reactor was built, and it performed well. The liquid fluoride approach was seen to work well with a thorium fuel process, because there was the potential to continuously process the fuel and blanket salts. Much of the chemical processing would be relatively inexpensive, because much of the chemistry for the process was fairly simple and well understood within the nuclear industry.

As Oak Ridge scientists studied the potential of a reactor used nuclear fuel suspended in liquid fluoride salts, they found more and more to like about it. It was far far safer than LWR. It could produce from thorium, an atom of fissionable U233, for every atom of U233 it burned. Some fission products could be easily removed from the reactor, while others radioactive isotopes could remain in the reactor salts fluid, until the reactor was removed from service. At that point they could be processed out of the salt fluid, and after loosing their radioactivity, the many valuable materials that had been produced by the nuclear process, could be recycled into industry. Thus the supposed problem of nuclear waste could be solved.

Political opposition by government bureaucrats and powerful members of Congress eventually killed research into a Liquid Fluoride Thorium Reactor (LFTR). Many scientist, however, continued to believe that the LFTR has many unique advantages. In his last paper (Thorium fueled underground power plant based on molten salt technology, ), Edward Teller wrote,

"Our economic goal is to achieve a cost of electrical energy averaged over the life of the power station to be no more than that from burning fossil fuels at the same location. Past studies have shown a potential for the molten salt reactor to be somewhat lower in cost of electricity than both coal and LWRs. There are several reasons for substantial cost savings: low pressure operation, low operations and maintnance costs, lack of fuel fabrication, easy fuel handling, low fissile inventory, use of multiple plants at one site allowing sharing of facilities, and building large plant sizes. The cost of undergrounding the nuclear part of the plant obviously needs to be determined and will likely not offset the cost advantages of a liquid-fueled low-pressure reactor."

In a separate research proposal (Deep-Burn Molten-Salt Reactors ), Ralph Moir of Lawrence Livermore National Laboratory, who co-authored Teller's last paper, togeather with T. J. Dolan, of Idaho National Engineering and Environmental Laboratory, Sean M. McDeavitt of Argonne National Laboratory, D. F. Williams and C. W. Forsberg of Oak Ridge National Laboratory, and E. Greenspan and J. Ahn of the University of California, Berkeley wrote,

"Molten salt reactors have the potential of meeting the goals of Generation IV reactors
better than solid fuel reactors. They also have the potential of meeting the goals of the
high-level waste transmutation program better than solid fuel reactors. In fact, they may
enable doing most if not all of the transmutation planned for accelerator-driven
subcritical reactors."

3 comments:

Anonymous
said...

Another excellent post!

You make a very persuasive case for molten fluoride reactors as the best long term option for the thorium fuel cycle, but finding a way to use thorium in existing reactor designs seems like the best way of promoting thorium use in the shorter term.

Do you think the uranium/thorium seed/blanket model tested in the Shipping port reactor could be adapted for current commercial LWRs?

I’ve also seen claims that CANDUs can achieve “near breeder” status with thorium, but I haven’t yet been able to track down any original references giving actual conversion ratios.

Finally, the World Nuclear Association website article on thorium suggested that there were some unresolved technical problems (besides U-232 and Th-228 contamination) with reprocessing spent thorium fuel to reclaim U-233. Is there something about thorium’s chemistry that makes it more difficult to reprocess than spent uranium fuel?

Thanks in advance. Your blog is a valuable educational resource on this topic.

In oxide form, thorium is significantly more difficult to reprocess than uranium oxide, which itself is already difficult to reprocess.

This is yet another reason for fluoride reactors to exploit the thorium resource. There simply isn't an economic advantage to using thorium in solid-fueled reactors like LWRs and CANDUs.

In any low- or natural-enrichment reactor (like LWRs and CANDUs) thorium will have to displace U-238 (which is also fertile). That will simply require greater levels of enrichment, which are expensive for LWRs and CANDUs. In the case of CANDUs, going to any level of enrichment negates much of the original argument for the reactor.